https://www.mudlet.org/ is a client with a lot of muds to choose from. You can also connect to others of course.
I still play https://mume.org/ from time to time. It's been running (almost) continuously since 1991. I started it in 1992.
My favorite MUD is definitely Midnight Sun II. It's one of the MUDs in the selection you get when you start Mudlet from mudlet.org, which is an excellent/modern client.
http://www.eotl.org/ was great in the 80s and was still great when I played a few years ago.